1. Field of the Invention
The present invention relates to an electrode for a rechargeable lithium battery and a rechargeable lithium battery fabricated therefrom.
2. Description of the Related Art
Rechargeable lithium batteries have recently drawn attention as power sources for small portable electronic devices. These batteries use organic electrolyte solutions and therefore have twice the discharge voltage of a conventional battery using an alkali aqueous solution. Accordingly, lithium rechargeable batteries have high energy density.
Lithium-transition element composite oxides being capable of intercalating lithium, such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), LiMnO2, and so on, have been researched for use as positive active materials in rechargeable lithium batteries.
Lithium metals have been used as negative active materials in rechargeable lithium battery. However, the cycle-life (or lifespan) of the batteries may be shortened due to formation of dendrites when the lithium metals are used. Therefore, carbonaceous materials, such as amorphous carbon, crystalline carbon, etc., have recently been used as the negative active materials in place of lithium metals. The carbonaceous negative active materials can inhibit the formation of dendrites, provide relatively flat voltage characteristics at relatively low potentials, and have good cycle-life characteristics. However, a carbonaceous negative active material has relatively high reactivity with an organic electrolyte solution, and a relatively high diffusion rate of lithium. As such, in a rechargeable lithium battery with a carbonaceous negative active material, the electric power characteristics, initial irreversible capacity, and electrode swelling at charge and discharge need to be controlled. In addition, there is a need to improve energy density of a rechargeable lithium battery. In order to improve cycle-life, a lithium alloy may be used as a negative active material. For example, a negative electrode may include a metal not alloyed with lithium and a metal alloyed with lithium. Here, the metal not alloyed with lithium acts as a current collector, and the metal alloyed with lithium forms an alloy with lithium ions that are released from a positive electrode during charging. Therefore, the negative electrode includes lithium during charging, and the alloy functions as a negative active material. However, the lithium alloy cannot provide satisfactory battery characteristics.
In addition, metal negative active materials such as silicon (Si), tin (Sn), a compound including Si or Sn, etc. may be used as a substitute for the carbonaceous material. However, the Si or Sn has a relatively large irreversible capacity problem. Particularly, Si undergoes serious shrinkage or expansion during charge and discharge and thereby a Si negative active material may be detached resulting in deterioration of cycle-life of the rechargeable lithium battery. Tin oxide may also be used as an alternative to the carbonaceous negative active material. However, the metal negative active material has 30% or less initial Coulomb efficiency. Further, as lithium is continuously intercalated and deintercalated to generate a lithium-metal alloy, the capacity and cycle-life are decreased and therefore it has not yet been commercialized.